There is a race window in dlm_get_lock_resource(), which may
return a lock resource which have been purged. This will cause
the process hung forever in dlmlock() as the ast msg can't be
handled due to its lock resource not exist.
dlm_get_lock_resource {
...
spin_lock(&dlm->spinlock);
tmpres = __dlm_lookup_lockres_full(dlm, lockid, namelen, hash);
if (tmpres) {
spin_unlock(&dlm->spinlock);
>>>>>>>> race window, dlm_run_purge_list() may run and purge
the lock resource
spin_lock(&tmpres->spinlock);
...
spin_unlock(&tmpres->spinlock);
}
}
Signed-off-by: Junxiao Bi <junxiao...@oracle.com>
Cc: Joseph Qi <joseph...@huawei.com>
Cc: <sta...@vger.kernel.org>
---
fs/ocfs2/dlm/dlmmaster.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/fs/ocfs2/dlm/dlmmaster.c b/fs/ocfs2/dlm/dlmmaster.c
index a6944b2..fdf4b41 100644
--- a/fs/ocfs2/dlm/dlmmaster.c
+++ b/fs/ocfs2/dlm/dlmmaster.c
@@ -757,6 +757,19 @@ lookup:
if (tmpres) {
spin_unlock(&dlm->spinlock);
spin_lock(&tmpres->spinlock);
+
+ /*
+ * Right after dlm spinlock was released, dlm_thread could have
+ * purged the lockres. Check if lockres got unhashed. If so
+ * start over.
+ */
+ if (hlist_unhashed(&tmpres->hash_node)) {
+ spin_unlock(&tmpres->spinlock);
+ dlm_lockres_put(tmpres);
+ tmpres = NULL;
+ goto lookup;
+ }
+
/* Wait on the thread that is mastering the resource */
if (tmpres->owner == DLM_LOCK_RES_OWNER_UNKNOWN) {
__dlm_wait_on_lockres(tmpres);
--
1.7.9.5
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